An ongoing effort to reduce drag in vehicular structures is of great importance as fuel economy becomes an increasingly large consideration in vehicular design. As the drag of a vehicle increases, the amount of fuel needed to move the vehicle also increases due to the greater energy required to overcome the drag. For instance, it has been stated that for a vehicle traveling at 70 mph, about 65% of the total fuel consumption of the vehicle's engine is used to overcome drag. Therefore, even a small reduction in the drag experienced by a vehicle traveling at highway speeds can result in a significant improvement in fuel economy.
For instance, heavy-duty vehicles such as tractor-trailers (also known as semi tractors, tractors, class 8 long haul trucks, transfer trucks, 18-wheelers, semis, etc.) have a tall and wide box-shaped profile that creates a significant amount of drag compared to smaller vehicles on the road. For instance, Table I lists common drag coefficients of road vehicles.
TABLE IType of VehicleDrag Coefficient (Cd)Low Drag Production Car.26Typical Sedan .3-.35Sport Utility Vehicle.4-.5Pick-up Truck.4-.5Conventional Class 8 long haul tractor trailers.59-.63
In the U.S., vehicles commonly used to move freight typically include a tractor which powers the vehicle and a trailer which contains the freight. Tractors usually have 3 axles, the front, or “steer”, axle having two wheels, and two rear, or “drive”, axles each having a pair of wheels on each side. The most common configuration of this type of tractor has 10 wheels; however, in some cases the traditional pairs of wheels and tires are replaced by single wides; also known as “super singles”, or wide-base singles. Single wide tires and wheels reduce the weight of the semi-trailer and in some cases reduce the rolling resistance of the vehicle. Tractors equipped with single wides only have six tires and wheels. Smaller tractors, having a single drive axle (for 6 wheels in total) are often used to pull shorter trailers in tight urban environments. The tires, wheels, axles, drive shaft, differentials, and other wheel components also create drag.
Cargo trailers have a similarly tall and wide box-shaped profile that creates drag because the enclosed cargo space of a trailer is often rectangular in shape. The most common type of cargo trailer in the U.S. is a dry box van that is 53 feet long. Most common cargo trailers typically have two “tandem” axles at the rear, each of which has a pair of wheels for 8 wheels on the trailer. Tires and wheels on trailers can also be replaced with single wides, reducing the total number of tires and wheels on the trailer from 8 to 4. Again, the tires, wheels, axles, and other wheel components create drag. A cargo trailer also typically includes landing gear, which includes legs that the trailer rests upon when detached from a tractor. The landing gear can also create drag.
Certain devices are known in the art, such as trailer sideskirts, fairings, trailer end caps, boat tails, and the like, which attempt to address certain areas of drag on a vehicle. However, many of these devices have significant limitations in their ability to reduce drag or their ability to be easily integrated into fleet operations. As a result, a comprehensive solution for improving drag on a vehicle is still needed.
Thus, a need exists for devices that are designed to provide drag reduction for a vehicle trailer. Methods relating to the utilization of such devices would also be beneficial. Retrofit kits for incorporating such devices into vehicles would also be beneficial.